The photoconductive process for electrophotographic light-sensitive materials is generally considered to include
(1) a step of generating an electric charge pattern by exposing a material to light, and
(2) a step of transporting electric charges.
As an example of conducting the steps (1) and (2) in the same substance, there is a selenium light-sensitive plate. On the other hand, as an example of conducting steps (1) and (2) in different substances, a combination of amorphous selenium and poly-N-vinylcarbazole have been well known. The process in which the steps (1) and (2) are conducted with different substances has advantages, such as that the range of selection of materials that can be used for the light-sensitive material is expanded, and, consequently, electrophotographic characteristics such as sensitivity, receiving electric potential, etc., of the light-sensitive materials are improved, and substances advantageous for producing a coating film of the light-sensitive material can be selected from a wide range.
Substances that have hitherto been used as photoconductive raw materials for light-sensitive materials to be used in the electrophotographic process include inorganic substances such as selenium, cadmium sulfide, zinc oxide, etc.
As disclosed by Carlson in U.S. Pat. No. 2,297,691, the electrophotographic process uses a photoconductive material comprising a support coated with a substance which is electrically insulating in the dark, the electric resistance of which changes according to the amount of exposure to which it is subjected during imagewise exposure. Uniform surface electric charges are provided on the photoconductive material in the dark, generally, after carried out dark adaptation for a suitable period of time. This material is then imagewise exposed to light with an irradiation pattern having an effect of reducing surface electric charges according to relative energy contained in various parts of the irradiation pattern. The surface electric charges or electrostatic latent image remaining on the surface of the photoconductive substance layer (light-sensitive layer) is then brought into contact with a suitable electroscopic indicating substance, referred to as a toner, to form a visible image. The toner can be allowed to adhere to the surface of the light-sensitive layer according to the electric charge pattern regardless of being contained in an electrically insulating liquid or in a dried carrier. The indicating substance adhering to the surface can be fixed by known means such as heat, pressure, or solvent vapor. The electrostatic latent image can be transferred to the second support (for example, paper or film, etc.). The electrostatic latent image can be developed on the second support after it is transferred thereto. The electrophotographic process is any image forming process in which an image is formed as in the above described manner.
In such an electrophotographic process, fundamental characteristics required for the light-sensitive materials are that: (1) electrification can be carried out in the dark so as to have a suitable electric potential, (2) disappearance of electric charge in the dark is small, and (3) the electric charge can be rapidly removed by exposing to light. The above described inorganic substances used hitherto have various faults, although simultaneously with having many advantages. For example, selenium, which is widely used at present, sufficiently satisfies the above described requirements (1)-(3), but it has faults in that production thereof requires severe conditions which increase cost for production, it is difficult to form a belt shape because of lack of flexibility, and it requires careful handling because it is sensitive to heat and mechanical impact. Cadmium sulfide and zinc oxide have been used as light-sensitive materials by dispersing in a binder resin. However, they can not repeatedly used in such a state to the desired extent, because of mechanical faults that develop with respect to smoothness, hardness, tensile strength, friction resistance, etc.
In recent years, for the purpose of overcoming these faults of inorganic substances, electrophotographic light-sensitive materials using various kinds of organic substance have been proposed, and some of them have been put in practical use. For example, there are light-sensitive materials composed of poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-one (described in U.S. Pat. No. 3,484,237), those wherein poly-N-vinylcarbazole is sensitized with a pyrylium salt type dye (described in Japanese Patent Publication No. 25658/73) and light-sensitive materials comprising an eutectic crystal complex composed of a dye and a resin as a main component (described in Japanese Patent Application (OPI) No. 10735/72), etc. (the term "OPI" as used herein refers to a published unexamined Japanese Patent Application).
Further, high-speed electrophotographic light-sensitive materials comprising a combination of a substance which generates an electric charge by light (hereinafter referred to as an electric charge generating substance and a substance which can convey the formed electric charge (hereinafter referred to as an electric charge transporting substance) have been proposed. For example, light-sensitive materials in which an electric charge transporting layer is provided on an electric charge generating layer are described in U.S. Pat. No. 3,791,826, light-sensitive materials in which an electric charge generating layer is provided on an electric charge transporting layer are described in U.S. Pat. No. 3,573,906, and light-sensitive materials having a light-sensitive layer in which an electric charge generating substance is dispersed in an electric charge transporting substance are described in U.S. Pat. No. 3,764,315. With respect to light-sensitive materials of this type, various electric charge generating substances have been proposed, but there has been no proposal of really useful electric charge transporting substances. A good electric charge transporting substance (1) which allows sufficient transmission of light having wave-lengths generate electric charges in the electric charge generating substance to pass through it to the electric charge generating substance, (2) sufficiently retains an electric potential when electrified, and has an ability of rapidly transporting electric charges generated in the electric charge generating substance.
As a result of extensive studies, the present inventors have found that hydrazone compounds represented by formulae (I), (II), and (III) described hereinafter are really useful electric charge transporting substances for electrophotographic light-sensitive materials, and thus the present invention has been attained.
Examples of hydrazone compounds used as electrophotographic light-sensitive materials are disclosed in U.S. Pat. No. 3,717,462 (corresponding to Japanese Patent Publication No. 8137/73), Japanese Patent Application (OPI) Nos. 59143/79 (corresponding to U.S. Pat. No. 4,150,987), 52063/80 (corresponding to U.S. Pat. No. 4,338,388) and 52064/80, etc. However, these compounds are condensed polynuclear substances or N-alkylamino substituted substances.
The present inventors have already found that electrophotographic light-sensitive materials having a light-sensitive layer containing N-arylamino substituted substances are remarkably improved in stability to oxidation caused by ozone generating by corona discharging, which is a fatal drawback of the above described known light-sensitive materials, stability to light and heat, dark decay properties, etc., and they have characteristics that sensitivity is high, residual electric potential which causes fog is low, variation of residual electric potential or sensitivity caused by repeated use is small, and durability is excellent. Thus, they have been proposed as inventions in Japanese Patent Applications (OPI) Nos. 11350/82 and 104144/82 (corresponding to U.S. Pat. Nos. 4,403,025 and 4,396,694, respectively. The present invention provides electrophotographic light-sensitive materials having excellent characteristics similar to the above described prior inventions, by using novel hydrazone derivatives having a dimer structure.